The present invention, in some embodiments thereof, relates to photon pair generation and its applications.
Quantum entangled photon pairs can be used for quantum information processing, including quantum cryptography, quantum computing and quantum teleportation, as described, for example, by C. Bennett and S. J. Weisner, Phys. Rev. Lett. 69, 2881 (1992); P. Kumar et al, Quantum Inf. Process. 3, 215 (2004); Z. D. Walton et al, Phys. Rev. A, 67, 062309 (2003); and J. F. Clauser et al, Phys. Rev. Lett. 23, 880 (1969). Quantum entangled photon pairs can also be used for very low noise spectroscopy (including in vivo spectroscopy) and microscopy, as described, for example, by Saleh et al., Phys. Rev. Lett. 80, 3483 (1998) and by U.S. Pat. No. 5,796,477 to Teich et al.
Pairs of quantum entangled photons can be produced by using two photon emission from certain atomic radiative cascades, as described, for example, by A. Aspect, P. Gragnier and G. Roger, Phys. Rev. Lett. 47, 460 (1981), but these sources suffer from low brightness and polarization degradation caused by the atomic recoil.
Solid state sources of entangled photon pairs, based on parametric down conversion (PDC) of pump photons, for example in non-centrosymmetric crystals with second-order optical nonlinearity, have higher emission rates, and are described, for example, by P. G. Kwiat et al, Phys. Rev. Lett. 75, 4337 (1995), by M. Pelton et al, Opt. Express 12, 3573 (2004), and by X. Li et al, Phys. Rev. Lett. 94, 053601 (2005). But these sources have relatively low efficiency because they use post-selection or spatial filtering, and are based on a third-order (in the fine structure constant α) non-resonant process in the time-dependent perturbation theory. PDC sources typically require pump lasers of high power, are bulky, and use exotic materials. The pump lasers typically used cost over $100,000.
Semiconductor quantum dots can also produce pairs of entangled photons, by single photon emission from pairs of entangled electrons, as described for example by N. Akopian et al, Phys. Rev. Lett. 96, 130501 (2006), and they are more efficient than PDC sources. However, quantum dot sources have low generation rates, their emission wavelengths are not tunable, currently only optical excitation is implemented and they require cryogenic temperatures, typically lower than 20 K. An article by Rupert Goodwins, dated Jan. 11, 2006 and downloaded from the internet at http://news.zdnet.com/2100-1009—22-6026098.html, on Nov. 18, 2007, quotes Andrew Shields, head of the Quantum Information group at Toshiba Research Europe, as saying that there is no reason in principle why quantum dots could not produce entangled pairs of photons at room temperature, but states that there are still challenges to be overcome before achieving such a device.
Two-photon amplifiers and lasers are described, for example, by C. N. Ironside, IEEE J. of Quantum Elect. 28, 842 (1992); C. Z. Ning, Phys. Rev. Lett. 93, 187403 (2004); D. H. Marti et al, IEEE J. of Quantum Elect. 39, 1066 (2003); and D. R. Heatley et al, Opt. Lett. 18, 628 (1993). Heatley et al describe using two-photon amplifiers and for pulse generation, because the gain in two-photon lasers/amplifiers, in contrast to conventional single photon lasers, is nonlinear, depending on the amplitude of the light wave.
Two photon absorption in semiconductors has been investigated, for example, by V. Nathan et al, J. Opt. Soc. Am. B 2, 294 (1985); C. C. Lee and H. Y. Fan, Phys. Rev. B 9, 3502 (1974); N. G. Basov et al, J. Phys. Soc. Japan Suppl. 21, 277 (1966); D. C. Hutchings and E. W. Van Stryland, J. Opt. Soc. Am. B 9, 2065 (1992); and M. Sheik-Bahae et al, IEEE J. Quantum Electron. 27, 1296 (1991).
The disclosures of the above mentioned documents are incorporated herein by reference.